Modern linear motion guide units in recent years are demanded to increasingly improve the highly-tight sealing performance to keep any foreign matter away from entering inside the slider, ensuring maintenance-free operation for lubricant and coping with high-speed sliding movement of the slider. Thus, with the conventional linear motion guide units, the end seal equipped on the slider is designed to increase the interference for sealing or have a double lip-type construction composed of inward and outward seals. One of the prior linear motion guide units as shown in FIG. 22 (A) has a guide rail 1 and a slider 2P that is allowed to move relative to the guide rail through rolling elements. The slider 2P is composed of a carriage, end caps 4P secured on lengthwise ends of the carriage, one to each ends, and end seals 6P arranged on outward end surfaces 14P of the end caps 4P. The end seals 6P are each composed of an elastic member 7P and a metallic core 8P serving as a skeleton of the end seal 6P to reinforce or bear the elastic member 7P. With the elastic member 7P, there is provided the double lip-type sealing construction 19P made up of an outside lip 21P extending outward of the slider 2P to make sliding engagement with a top surface 10 of the guide rail 1 and an inside lip 22P extending inward of the slider 2P.
There has been already known a linear motion guide system with a sealing device, which is disclosed in, for example Japanese Laid-Open Patent Application No. 2011-247 359. With the prior linear motion guide system, the sealing device is composed of a lip-type seal and a protector to squeeze the lip-type seal to exclude foreign material from between the lip-type seal and the protector while exerting adequate sealing impact on the lips of the seal. A first lip of the lip-type seal is made raised above a major portion of the seal to undergo elastic deformation after the protector has been fastened to the lip-type seal. As a result, the first lip is urged against a surface of a guide rail to make close engagement with the protector around a U-shaped open edge of the protector.
In Japanese Laid-Open Patent Application No. 2002-266 858, there is disclosed another linear motion guide system with a side seal construction, whose a pair of outside and inside lips is protected from any excessive deformation when the sliders moves, so that the linear motion guide system is expected to ensure better sealing quality and retention of lubricant for a prolong period even in worse working environment where much foreign matter occurs. The side seal construction in the prior linear motion guide unit is mounted on one end of the slider with the lips apart from each other to make sliding contact with the outside surface of the guide rail, thereby defining a V-shaped gap between the lips in a travelling direction of the slider. The outward lip serves to exclude dirt and the inward lip retains lubricant inside a space defined with the lips, the surface of the guide rail and the concaved inside surface of the slider. The lips in transverse section are arranged in plane symmetry relative to a plane perpendicular to the outside surface of the guide rail. A core member of the side seal construction is placed in a relation that a center line in thickness direction extends coincidentally with the plane perpendicular to the outside surface of the guide rail into the lips to bear or back the lips. As an alternative of the side seal construction stated earlier, the lips are biased or deflected away from the end cap by a spacer part or bending of the core member to isolate the lips from the end cap to prevent any interference of the lips with the end cap.
With the linear motion guide unit constructed as stated earlier, the outward lip 21P of the double lip-type construction 19P when the slider 2P moves relative to the guide rail 1 as shown in FIG. 22(B) undergoes no deformation because the outward lip 21P is born against the metallic core 8P lying on the center line CL of the outward lip 21P. On the other hand, the inward lip 22P is pressed down against the top surface 10 of the guide rail 1 to collapse so that the lubricant existing on the top surface 10 would leak out of the slider 2P. Thus, the linear motion guide unit constructed as stated earlier has an unsatisfactory result in demand for air-tightness and fails in maintenance-free operation because of leakage of lubricant, with causing an issue of lowering the sliding performance.
Moreover, it is said that the linear motion guide unit cited earlier has the same fault as in the construction described with reference to FIG. 22(B). The elastic lips, as extending long from the metallic core to the leading edge, are liable to bend or warp largely. Thus, the inward lip when suffered to a force opposite to an extending direction of the inward lip undergoes deformation to pose a problem of lubricant leakage. The outward lip is pressed with a protector to undergo the elastic deformation to make the air-tight engagement with the surface of the guide rail, whereas the inward lip is free from any support of a metallic plate and therefore liable to cause any warp when suffered to the external force.